The use of multiple light emitting diodes (LEDs) becomes more and more common for creating the required amount of light for displays such as TVs and monitors. The LEDs usually form a panel referred to as a backlight device, which is intended to provide a homogenous light to the back surface of the display. LEDs of different colours are usually put in clusters so that the combined light of the cluster meets specific demands, e.g. such that the mixed light from the LEDs of each cluster form the same target white point. As an example, clusters or rows of RGBG-coloured LEDs may be used, in which R refers to a red LED, G refers to a green LED and B refers to a blue LED.
Most backlights are either “edge-lit” or “back-lit”, which differ in the placement of the LEDs relative the display. In an edge-lit backlight, the LEDs are positioned along the border of the backlight, and a light guide is used to direct the light from the LEDs such that the display is illuminated, whereas the LEDs of a back-lit backlight (also referred to as a “direct-lit” backlight) are positioned directly behind the display or output area. There are growing demands for increasing the gamut, or colour gamut, of displays while at the same time decreasing the bezel, which is the dark edge around the active area of the display. Further, there are growing demands in making the displays as slim as possible. However, problems arise when all these demands are to be met. For example, the colour of the individual LED nearest the edges of the display is usually visible when viewing the display, due to insufficient colour mixing at the edge. In an RGBG system, this may for example result in a display having too much red at one edge and too much green at the opposite edge. In a backlit backlight, the corners of the display may have colours that even further deviates from a selected white point due to the insufficient colour mixing.
A solution to this problem is proposed in U.S. Pat. No. 7,671,832, in which the white point of the clusters of LEDs at the edges are colour-shifted based on the centers of gravity of the colours of the clusters, i.e. the effect is minimized by shifting the colour of the cluster at the edge to the opposite colour.